Elon Musk, who owns X, the social media platform formerly known as Twitter, announced on Thursday that his company plans to take legal action against those involved in what he describes as an “advertising boycott racket.”

Mr. Musk’s declaration came after watching a video of Ben Shapiro, co-founder of the Daily Wire, testifying before the House Judiciary Committee during a session titled “Collusion in the Global Alliance for Responsible Media” on Wednesday.

“Having seen the evidence unearthed today by Congress, 𝕏 has no choice but to file suit against the perpetrators and collaborators in the advertising boycott racket,” Mr. Musk wrote on his social media platform. “Hopefully, some states will consider criminal prosecution.”

Mr. Shapiro laid out a slew of facts that illustrate how advertisers boycott conservative news sites.

“We’re in the midst of a trust crisis in the world of media, which is because so many in the legacy media have lied in order to preserve left-leaning narratives,” he said.

“The question isn’t really why the legacy media have lost Americans’ trust. We know that answer. The question is why — despite that loss of trust — the legacy media continue to gain share in the advertising market. And the answer is simple. There is, in fact, an informal pressure system created by Democratic legislators, this White House, legacy media, advertisers, and pseudo-objective brand safety organizations. That system guarantees that advertising dollars flow only to left-wing media brands,” Mr. Shapiro said.

The author and podcast host cited the left-wing informational safety group Global Alliance for Responsible Media, which he said “sets brand safety standards, objective standards by which advertisers and platforms can supposedly determine just what sort of content ought to be deemed safe for advertising.”

“Companies targeted by GARM, like the Daily Wire, Breitbart, Fox News, and so many others, reach hundreds of millions of people with opinions and beliefs long established as within the mainstream of American conservative thought. GARM and its members have no respect for the beliefs of those people. They would like them marginalized or squashed. It’s time to stand up for the First Amendment in this Congress,” he said.

Mr. Shapiro said Congress should investigate “the informal and perhaps formal arrangements between censorship cartels like GARM and executive branch agencies.” And he said lawmakers should “stop engaging in violation of free speech principles.”

“We all know what these government actors, what some people in this room are doing. You’re using the tacit threat of government action to compel private companies to throttle viewpoints you don’t particularly like. The First Amendment was not designed to enable workarounds by elected officials. It was directed at Congress, at you,” he said.

“And you’re abdicating your fundamental duty when you exert pressure on private companies to censor speech,” Mr. Shapiro said. “Some in this room have been doing just that for years. We in the non-legacy media have been feeling the effects. In the name of the Constitution and the name of democracy, this should stop.”